Methyl mercaptan (MeSH) can be produced on a commercial scale via the following reaction in the presence of a catalyst:methanol(CH3OH)+hydrogen sulfide(H2S)→methyl mercaptan(CH3SH)+water(H2O).
Examples of processes for producing MeSH by reacting hydrogen sulfide and methanol are described in U.S. Pat. Nos. 2,822,400 and 3,792,094. Depending on the purity of the feedstocks and reaction conditions, a reaction effluent can include the desired methyl mercaptan and other compounds which can include but are not limited to methanol (MeOH), hydrogen sulfide (H2S), hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), light hydrocarbons, dimethyl sulfide (DMS), dimethyl disulfide (DMDS), water (H2O), mercaptans with a higher carbon number than MeSH, or combinations thereof. Processes for producing methyl mercaptan can include various separation techniques for isolating the methyl mercaptan from any of the above mentioned compounds in the reaction effluent, as well as separation techniques for isolating any of the compounds from one another. Various streams can be obtained by the separation techniques, for example, a stream containing mostly DMS, a stream containing mostly H2S, and a stream containing mostly MeSH can be recovered from the processes.
DMS in particular can be present in the reaction effluent as a by-product of the reactions. For example, DMS can be produced via the following reactions in the presence of the same catalyst:methanol(CH3OH)+methyl mercaptan(CH3SH)→dimethyl sulfide(DMS)+water(H2O)ormethyl mercaptan(2CH3SH)→dimethyl sulfide (DMS)+hydrogen sulfide(H2S).
Historically, formation of DMS has been less desirable than formation of MeSH. However, depending on operating conditions, the amount of DMS produced can still exceed 10 wt % of the MeSH produced in the reactions. While DMS can have some value at certain purities under certain market conditions, thus justifying isolation of DMS in a stream dedicated for DMS recovery, MeSH can have a higher value. Moreover, even when it is desired to isolate and recover DMS, prices can fall due to oversupply.